The use of emissive displays such as organic light emitting diodes (OLEDs) on portable telephones and data devices are well known. Such displays allow an operating system within the telephone or data device to display status of operation and data to a user.
In the case of incoming calls, the display may inform the user of the identity of a caller. In the case of outgoing calls, the display may provide the user with an entered telephone number in order to allow the user to correct mistakes.
In the case of a portable device, the display may show a battery monitor that indicates a battery charge status. As the battery reaches a critical level the battery monitor may flash to notify the user of the need to recharge or suspend use.
In the case of portable telephones or data devices, status indicators are typically displayed in a single, respective location on the display for the convenience of the user. For example, a battery status indicator may be displayed in an upper right corner. Alternatively, the status indicator “CALLING” may be displayed in a center as may the words “SHUTTING DOWN” to indicate deactivation of the cell phone.
In general, emissive displays can experience a burned-in brightness or luminance modulation extending across the display caused by showing the same image over prolonged periods of time. The lifetimes of phosphors creating the image are finite and the luminance will decrease with time. As a result, when a different image is shown over the burned-in image, there will be local variations in luminance.
The luminance of many emissive displays decreases the more they are used. As the burned-in modulation increases, the display can become difficult if not impossible to read. Because of the importance of emissive displays a need exists for methods of ameliorating the effects of burn-in.